High performance integrated circuit (IC) packages are well known in the art. Improvements in IC packages are driven by industry demands for increased thermal and electrical performance and decreased size and cost of manufacture
In general, array packaging such as Ball Grid Array (BGA) packages provide a high density of interconnects relative to the surface area of the package. Typical BGA packages include a convoluted signal path, giving rise to high impedance and an inefficient thermal path which results in poor thermal dissipation performance. With increasing package density, the spreading of heat generated by the device is increasingly important.
Direct connection of the semiconductor die to a substrate surface in a flip-chip orientation, using solder ball connections provides low impedance packages relative to the use of wire-bond connections and provides reduced package space. This technology is becoming increasingly popular with package fabrication advances including advances in forming and placing of solder balls in flip-chip packaging.
FIG. 1 shows a sectional view of a conventional flip-chip BGA package indicated generally by the numeral 20. The flip-chip BGA package includes a substrate 22 with a semiconductor die 24 mounted in a flip-chip orientation, to a first surface of the substrate 22. Solder balls 26 provide electrical connections between the semiconductor die 24 and the substrate 22. Solder balls 28, in the form of a ball grid array are disposed on the second surface of the substrate. These packages suffer disadvantages, however.
One particular disadvantage is the generation of thermally induced stress in these packages, due to a mismatch in coefficients of thermal expansion (CTE) between the semiconductor die and the motherboard, when the package is in use. During temperature cycling, the CTE mismatch creates stresses and strains which are concentrated in the solder ball interconnects between the die and the substrate and in the semiconductor die. In extreme cases, the semiconductor die warps and fatigue failure occurs in the solder ball interconnects.
Variations to the conventional flip-chip BGA have been proposed for the purpose of increased performance. In one exemplary variation, a metal heat spreader is fixed to the back of the semiconductor die to aid in the dissipation of heat. While heat is better dissipated in this package than in the conventional flip-chip BGA, described above, CTE mismatch between the semiconductor die and the motherboard, still cause stresses and strains that have deleterious effects on the package integrity.
Thus, further improvements in flip-chip ball grid array packages are desirable in order to meet industry demands for increased performance.